In recent years various raster microscopes using SQUID (Superconducting Quantum Interference Device) sensors have been developed. A magnetic sample is moved beneath the SQUID so that the local variations in the magnetic flux (magnetic field map of the sample) can be determined. Microscopes with high temperature superconductors (HTS) SQUIDS which operate at 77K are better for the measurement of magnetic fields of samples at room temperature than low temperature superconducting SQUIDS since for good field resolution and locality or position resolution, a reduced distance between the sample and the SQUID sensor is especially important. This distance limits the spatial resolution of SQUID microscopes to about 50 μm. To overcome this drawback, in SQUID microscopes, the SQUIDS are combined with ferromagnetic magnetic field conductors. These ferromagnetic field conductors generally have lengths of several millimeters and are formed as soft magnetic rods with a fine point or tip at the location of the sample.
From DE 195 19 480 A1, a magnetic field sensor has become known. This magnetic field sensor is comprised of a rod made from a soft magnetic ferromagnetic material with a tip or point and serving as a magnetic field conductor, as well as a DC-SQUID serving as the detector. A disadvantage here is that the magnetic field sensor is susceptible to noise fields since the entire rod, above all in the case of magnetic field distributions produced by current flow through the conductor strips, functions as an antenna. The length of the rod limits the spatial resolution of the sensor strongly.
From DE 199 15 226, a magnetic flux sensor has become known with a looped-shaped magnetic conductor and a detector formed as a DC-SQUID in which a magnetic flux arising in the magnetic field conductor can be registered. The magnetic field conductor comprises a high permeability foil or a thin film. A drawback of this magnetic flux sensor is also that it does not have a high spatial resolution.